It is generally known in the art that various underfloor or below-deck areas of certain types of passenger aircraft can be used by passengers or crew members during at least portions of a flight. For example, it is known to outfit sleeping compartment containers within the freight or cargo hold of an aircraft, such that these sleeping compartment containers provide sleeping areas for individual passengers.
Various arrangements are also known for air-conditioning the several fuselage spaces including the freight or cargo compartment spaces of known aircraft types. In order to air-condition the above mentioned sleeping compartment containers to be suitable for occupancy by individual passengers, the conditioned air that is blown into these sleeping containers is heated to the required room temperature by an electrical heater, or alternatively cooled to the required temperature by a suitable cooling arrangement. The blown-in supply air is made up of various air components, which include portions of recycled air that has been withdrawn or extracted out of the passenger area, recycled i.e. prepared for reuse, and then recirculated, while additionally being cooled to a predetermined temperature using suitable cooling devices, for example an aircraft skin heat exchanger that uses the very low ambient environmental temperature prevailing outside of an aircraft flying at a typical cruise altitude. In this context, only temperature reductions within a rather strictly limited temperature range can be carried out during such cooling process. While the energy requirements for operating the aircraft air-conditioning packs are necessarily provided in any event, the above described known system of preparing and supplying air into the below-deck spaces requires at least an increased provision of electrical energy for operating the heaters that are needed for raising the temperature of the supplied air to higher levels. Also, the load on the existing air-conditioning packs is increased. As a result, the total energy consumption is increased, and makes greater demands on the limited on-board energy resources of the aircraft, which in turn also increases the costs of operating the aircraft.
A general reference disclosing means for carrying out the air-conditioning of cabin spaces of a passenger aircraft is German Patent Publication 43 35 152 C1 and corresponding U.S. Pat. No. 5,516,330 (Dechow et al.), which also suggest measures for air-conditioning the underfloor or below-deck spaces of the aircraft, such as the electrotechnical and electronics areas and the freight compartment areas. The disclosed ventilation or recirculation system relates primarily to the air-conditioning and ventilation of the passenger and cockpit areas of the aircraft, while the underfloor area of the aircraft is connected to the same system.
A person of ordinary skill in the art of aircraft construction will recognize from the above mentioned publications, that an air mixer unit provides prepared mixed air to the passenger and cockpit areas of a passenger aircraft. In this context, the mixed air is made up of partial quantities of fresh air and of recycled used exhaust air. The recycled air comprises used air that is exhausted out of the passenger and cockpit areas and thereafter prepared for recirculation in a so-called cabin recycling unit, comprising a particle and/or odor filter unit, a blower unit, a carbon dioxide adsorber unit, and a heat exchanger unit. The resulting recycled or recirculation air is delivered to the mixer unit together with externally tapped fresh air, which is extracted as hot bleed air from the engines of the aircraft for example. The prepared recycled air and the hot bleed air are mixed in the mixer unit, and then the resulting mixed air is blown from the mixer unit into the passenger and cockpit spaces.
In the above context, the heat exchanger unit integrated into the recycling unit receives externally extracted cool exterior air, by means of which the recirculated exhaust air is cooled to a suitable or comfortable tempered temperature level before it leaves the recycling unit to be provided as so-called prepared recirculation air to the mixer unit. It is also suggested, that the mixed air is additionally post-tempered by admixing a further regulated or branched-off partial quantity of bleed air that is tapped from the engines, before the resulting tempered mixed air is introduced into the air-conditioned spaces, namely the passenger and cockpit spaces. The introduction of this post-tempering bleed air is controlled through a so-called trimming air control valve unit. This unit, which comprises two trimming air regulation valves, separately regulates the supply of the above-mentioned trimming air, on the one hand for the passenger space, and on the other hand for the cockpit.
The underfloor spaces or areas of the aircraft located below the main deck are only indirectly affected by the disclosed system, because it is merely suggested that the ventilation of the above-mentioned electrotechnical and/or electronics spaces and the freight compartment spaces is to be achieved by the leakage of conditioned air escaping from the cockpit space into the just mentioned underfloor spaces through leakage openings. In other words, the fresh air, or generally the supplied air, reaches the electrotechnical and electronics spaces as well as the freight compartment spaces only indirectly by penetrating through leakage openings. The air then leaves the freight compartment or cargo hold space either through an exhaust valve or through a fuselage leak, so as to penetrate out of the pressurized fuselage to the ambient exterior environment. This contemplated arrangement primarily relates to the compensation of leaks in the pressurized fuselage, even though it further aims to maintain the air quality in the aircraft cabin by supplying fresh air. Thereby, the supply of fresh air is only necessary for replacing the quantity of air that escapes the fuselage through fuselage leaks. The above-mentioned prior art reference does not suggest appropriate measures for the improved air-conditioning of underfloor areas of an aircraft while making rational and economic use of the available energy resources. The prior art reference also provides no suggestion toward prophylactic fire protection measures.